1. Field of the Invention
The present invention relates to an image reading apparatus. More particularly, it relates to an image reading apparatus used for making a reduced copy of figures, letters, etc drawn on a white board for example. The present invention also relates to a light conductor used for such an image reading apparatus.
2. Description of the Related Art
There are various kinds of image reading apparatuses used for reading images (figures, letters, etc) printed on a paper sheet or drawn on a white board. The optical system of such an image reading apparatus may include either selfoc (self-focusing) lenses or convex lenses for focusing the given original images onto the light receiving elements incorporated in the reading apparatus. The selfoc lenses, which are designed to perform a non-inverting and non-magnifying image-reading function, are preferably used for reading out the given images with high resolution. Generally, the selfoc lenses are more expensive than convex lenses. Thus, convex lenses are preferably used when high resolution is not required.
A conventional image reading apparatus disclosed in JP-A-2(1990)-273257 is shown in FIG. 15 of the accompanying drawings. The conventional apparatus includes a plurality of light receiving elements 91 mounted on a substrate 90, a plurality of convex lenses 92, and a light source (not shown) for illuminating the linear image reading region Sa. When the image reading region Sa is illuminated by the light source, the reflected light is converged by the convex lenses 92 to focus on the light receiving elements 91. The images received by the elements 91 are reduced-size, inverted images of the original (see an original arrow Oi and the focused arrow Ri). The light receiving elements 91 output image signals whose output levels correspond to the amounts of the received light.
Though conventional image reading apparatuses of the above type are widely used, they have been found disadvantageous in the following respect. As stated above, the conventional apparatus of FIG. 15 uses convex lenses 92 for its optical system. Thus, even if the image reading region Sa is uniformly illuminated by the light source, the image received by the light receiving elements 91 may be different in shade from the original, thereby failing to be the true image of the original. More specifically, referring to FIGS. 15 and 16, even if the original arrow Oi (see FIG. 15) is uniformly illuminated by the light source, the shade of the focused image Ri (see FIG. 16) may vary at positions. This is because light when passing through the convex lens 92 tends to be directed closer to the optical axis C of the lens 92. As a result, the central portion of D1 of the arrow Ri becomes brighter than its end portions D2, D3 (FIG. 16).
It is, therefore, an object of the present invention to provide an image reading apparatus which is capable of reproducing the true image of the original even if use is made of size-reducing lenses for the optical system.
Another object of the present invention is to provide a light conductor advantageously used in such an image reading apparatus.
According to a first aspect of the present invention, an image reading apparatus is provided. The apparatus comprises: a light source arranged to emit light for illuminating a linear image reading region extending in a primary scanning direction; a plurality of lenses arranged in an array for focusing light reflected on the image reading region and for producing reduced images, each of the lenses having an optical axis which intersects a predetermined portion of the image reading region; a plurality of light receiving elements for output of image signals based on the light focused by the lenses; and a light conductor for leading the light emitted by the light source toward the image reading region. The light conductor leads the emitted light so that said predetermined portion is illuminated more brightly than other portions of the image reading region which are adjacent to said predetermined portion.
According to a preferred embodiment, the light conductor includes a transparent member having a first surface and a second surface. The first surface faces the light source, while the second surface faces the image reading region. The transparent member is arranged to lead light from the first surface to the second surface so that distribution of light at the first surface is different from distribution of light at the second surface.
Preferably, the transparent member may be formed with a plurality of indents facing the image reading region. Each of the indents may be provided with an inclined portion slanted relative to the first surface of the transparent member.
According to a preferred embodiment, the transparent member may be formed with a plurality of projections facing the image reading region. Each of the projections may have a corner at which a cutout is provided.
The light source may include a plurality of light-emitting diodes arranged in an array. The light-emitting diodes may be offset in the primary scanning direction from the optical axes of the respective lenses.
Preferably, each of the light-emitting diodes may be held in facing relation to a relevant one of the inclined portions of the indents.
The image reading apparatus may further comprise a casing for supporting the light source, the lenses, the light receiving elements and the light conductor. The light conductor may protrude partially from the casing toward the image reading region.
According to a preferred embodiment, the first surface of the transparent member may be formed with a convex portion facing the light source.
According to another preferred embodiment, the light conductor may include a first transparent member and a second transparent member. Further, the light conductor may include more than two transparent members.
Preferably, the first transparent member may be provided with a light receiving surface facing the light source and a light emitting surface opposite to the light receiving surface. At least either one of the light receiving surface and the light emitting surface may be provided with a convex portion extending in the primary scanning direction.
According to a preferred embodiment, the second transparent member may be formed separately from the first transparent member. The second transparent member may be arranged to lead light emitted from the light emitting surface toward the image reading region.
Preferably, both the light receiving surface and the light emitting surface of the first transparent member may be convex.
Preferably, the second transparent member may be provided with a light receiving surface held in facing relation to the light emitting surface of the first transparent member.
According to a preferred embodiment, the light receiving surface of the second transparent member may be sinuous.
The image reading apparatus may further comprise light shielding members arranged between the light emitting surface of the first transparent member and the light receiving surface of the second transparent member.
Preferably, the first and the second transparent members may be fixed to each other. To this end, the first transparent member may be formed with a positioning groove, while the second transparent member may be formed with a leg portion fitted into the positioning groove of the first transparent member.
According to a second aspect of the present invention, there is provided a light conductor which comprises: a first surface for receiving light; a second surface for allowing the light to exit; and a plurality of indents defined by the second surface. Each indent is provided with an inclined portion slanted relative to the first surface.
According to a third aspect of the present invention, there is provided a light conductor which comprises: a first transparent member provided with a first light receiving surface and a first light emitting surface opposite the first light receiving surface, at least either one of the first light receiving surface and the first light emitting surface being formed with a convex portion; and a second transparent member formed separately from the first transparent member and provided with a second light receiving surface held in facing relation to the first light emitting surface of the first transparent member, the second transparent member being also provided with a second light emitting surface for allowing light to exit.
Other features and advantages of the present invention will become apparent from the detailed description given below with reference to the accompanying drawings.